Pyrenylpyridines: Sky-Blue Emitters for Organic Light-Emitting Diodes.

A novel sky-blue-emitting tripyrenylpyridine derivative, 2,4,6-tri(1-pyrenyl)pyridine (2,4,6-TPP), has been synthesized using a Suzuki coupling reaction and compared with three previously reported isomeric dipyrenylpyridine (DPP) analogues (2,4-di(1-pyrenyl)pyridine (2,4-DPP), 2,6-di(1-pyrenyl)pyridine (2,6-DPP), and 3,5-di(1-pyrenyl)pyridine (3,5-DPP)). As revealed by single-crystal X-ray analysis and computational simulations, all compounds possess highly twisted conformations in the solid state with interpyrene torsional angles of 42.3°-57.2°. These solid-state conformations and packing variations of pyrenylpyridines could be correlated to observed variations in physical characteristics such as photo/thermal stability and spectral properties, but showed only marginal influence on electrochemical properties. The novel derivative, 2,4,6-TPP, exhibited the lowest degree of crystallinity as revealed by powder X-ray diffraction analysis and formed amorphous thin films as verified using grazing-incidence wide-angle X-ray scattering. This compound also showed high thermal/photo stability relative to its disubstituted analogues (DPPs). Thus, a nondoped organic light-emitting diode (OLED) prototype was fabricated using 2,4,6-TPP as the emissive layer, which displayed a sky-blue electroluminescence with Commission Internationale de L'Eclairage (CIE) coordinates of (0.18, 0.34). This OLED prototype achieved a maximum external quantum efficiency of 6.0 ± 1.2% at 5 V. The relatively high efficiency for this simple-architecture device reflects a good balance of electron and hole transporting ability of 2,4,6-TPP along with efficient exciton formation in this material and indicates its promise as an emitting material for design of blue OLED devices.

Influence of Anion Variations on Morphological, Spectral, and Physical Properties of the Propidium Luminophore.

Propidium iodide (3,8-diamino-5-[3-(diethylmethylammonio)propyl]-6-phenylphenanthridinium diiodide, [P][I]), is a well-known red fluorescent dye that is widely used for biological applications such as staining. In this study, we have replaced the iodide counteranion of [P][I] with three hydrophobic and bulky organic anions, trifluoromethanesulfonate/[TfO], bis(trifluoromethanesulfonyl)imide/[NTf2], and bis(perfluoroethylsulfonyl)imide/[BETI], and have thus obtained a propidium-derived group of uniform materials based on organic salts (PGUMBOS). The morphological, spectral, and physical properties of these materials were investigated in order to understand the impact of anion variations. While [P][I] is a crystalline solid, propidium salts with [BETI] or [NTf2] counteranions, i.e., [P][BETI] and [P][NTf2], have significantly lower crystallinity as reflected in powder X-ray diffraction data. In addition, [P][BETI] and [P][NTf2] exhibited improved photothermal stability as compared to [P][I] when examined using thermogravimetric analysis and time-dependent kinetic fluorescence experiments under the given experimental conditions. Spectral and electronic properties of the propidium luminophore were not significantly changed upon anion variations, although fluorescence lifetimes and quantum yields showed a systematic increase with decreasing solvent polarity. The experimental HOMO-LUMO energy gaps of these compounds were ∼2 eV with energies of HOMO and LUMO orbitals obtained as -5.15 (±0.08) and -3.19 (±0.08) eV.

Effect of protic ionic liquid on the volumetric properties and taste behaviour of sucrose.

The volumetric properties and taste behaviour of sucrose in aqueous solutions of a protic ionic liquid (3-hydroxypropylammonium acetate) have been studied at temperatures, T=(293.15-318.15)K and at atmospheric pressure. Apparent molar volumes, V2,ϕ, apparent specific volumes, ASV, apparent molar isentropic compressibilities, Ks,2,ϕ, and apparent specific isentropic compressibilities, ASIC, were calculated from measured density, ρ and speed of sound, u data. Partial molar volumes, V2(°), and partial molar isentropic compressibilities, Ks,2(°) at infinite dilution, transfer parameters (ΔtV2(°) and ΔtKs,2(°)), expansion coefficients, [(∂V2(°)/∂T)P and (∂(2)V2(°)/∂T(2))P], interaction coefficients, (YAB and YABB) and hydration numbers, Nw, were also evaluated and discussed in terms of solute-cosolute interactions. Further, the effect of protic ionic liquid on the taste behaviour of sucrose has been discussed from ASV and ASIC parameters, as these parameters, which are sensitive to solvation behaviour of solute, are divided into four basic taste qualities occupying certain ranges.